Pipelines stop working after updating to MediatR 10.0 and .NET 6

[ShevchukDenys]

Hi! I have two pipelines behaviours: one with fluent validation and another with logging. So, after updating from MediatR 9.x to 10.0.1 I have faced the following issue: no validation or logging is triggered, in debugging it do not enter none of these classes. The changes I've done:

1. 
2. MediatR 9.0.0 => 10.0.1 & .net 5.0 => .net 6.0

[jbogard]

Try to isolate this in a test where you resolve from the container directly. The container package version changed too.

[ShevchukDenys]

It crashes with 'Sequence containes no elements' if I trying to get IPipelineBehavior or FluentValidationBehhavior directly from container, I suppose it means that this service isn't available in DI. As for container package I have updated it too, just forgot to mention.

[ShevchukDenys]

Also I have find out that it works if TResult is written explicitly, f.e.: Looks like it's similar to this: #182

[claudioscatoli]

I confirm that, with versions >=10.0, IPipelineBehaviour implementations need the generic constraint added, as per "Migration Guide 9.x to 10.0"

E.g.

public class CanonicalLogLineBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    //...
}

becomes

public class CanonicalLogLineBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IRequest<TResponse>
{
    //...
}

[rainerllera]

Hi all! Just wanted to give a +1 to this issue... since the where TRequest : IRequest<TResponse> constraint was added to IPipelineBehavior you can no longer wrap the responses in helper 'Result' classes or interfaces like the OP explained, unless you explicitly register the type... In my case I had:

ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, Result<TResponse>>

and was registering like usual (I'm using Autofac):

services.AddTransient<IPipelineBehavior<,>, ValidationBehavior<,>>();

After upgrading (and adding the constraint to the behavior in question) if I try to resolve IPipelineBehavior<TRequest, Result<TResponse>> directly from the container, it won't resolve. However, built-in behaviors like RequestPreProcessorBehavior, RequestPostProcessorBehavior are resolved correctly as IPipelineBehavior<TRequest, Result<TResponse>>, which I'm guessing has something to do with the calls to ConnectImplementationsToTypesClosing in MediatR.Registration.ServiceRegistrar's AddMediatRClasses method.

Now I'm not sure if this is a DI Container issue or a MediatR issue, since it does resolve if we register a validator for each command or query individually. Any alternatives/tips/workarounds would be great. Staying in v9 for now. Thanks!

[teggno]

@rainerllera I've had the same problem. It could be solved with

class ValidationBehavior<TRequest, TResult> : IPipelineBehavior<TRequest, TResult>>
   where TRequest: IRequest<TResult>

(In this case, TResult corresponds to Result<TResponse> which doesn't appear in the code explicitly but it still works.)

[wehnertb]

I had this for a definition:

public class CacheBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse> where TRequest : ICachable

Upgraded to .NET 6 and MediatR 10.0.1 and it won't compile.

Tried changing to :

public class CacheBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse> where TRequest : IRequest<TResponse>

And that doesn't work either - it compiles but fails at runtime. Finally uninstalled 10.0.1 and then regressed back to 9.0.0 and that works with .NET 6, but I don't know what else to do to get this to upgrade to 10.0.1.

Any suggestions would be greatly appreciated.

[jbogard]

Looks like you'd need two constraints:

public class CacheBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse> where TRequest : IRequest<TResponse>, ICachable

That compiles for me fine.

[wehnertb]

Thanks - that fixed it!

[plppp2001]

DO we need to add this where condition: [where TRequest: IRequest<TResult>]

It's working for me without the where for me.